1. Field of the Invention
The present invention relates to a wire bonding method and apparatus and more specifically to a method and apparatus for cutting a wire after a bonding is performed to a second bonding point.
2. Prior Art
FIG. 6 shows conventional wire bonding actions.
A capillary 3 and a wire cutting clamp 4 are moved up as shown in FIGS. 6(b) and 6(c) after a bonding wire 2 is bonded to a second bonding point 1 as shown in FIG. 6(a). In this case, the speed of the capillary 3 and wire cutting clamp 4 moving up is, as shown in FIG. 5(b), first increased as referred to by numeral 5 and then decreased as referred to by numeral 6.
While the moving up speed of the capillary 3 and wire cutting clamp 4 is accelerated at 5, the wire cutting clamp 4 is closed, thus cutting the wire from the attachment base of the second bonding point 1 as shown in FIG. 6(c). As a result of this cutting action, a certain length of wire (called the "tail" of wire) 2a is left below the tip of the capillary 3 so that a ball is formed at the end of the tail 2a in the next step.
The length of the tail 2a often affects the size and quality of the ball; accordingly, the tail length is extremely important in wire bonding. A wire cutting method of this type is described in Japanese Patent Application Publication ("Kokoku") No. 62-52948.
In this prior art, the wire cutting clamp 4 is moved up very fast while it cuts the wire. As a result, the timing of cutting the wires differs as shown by T1 in which the wire cutting clamp 4 is closed, and such a difference T1 causes a variance of S1 in the length S of the tail 2a as shown in FIGS. 5(a) and 5(c). Thus, tails of equal length are not always obtained. This variance in the tail length can be reduced if the moving speed at acceleration 5 is slowed down; however, this results in a long total wire cutting time.